Introduction 

West Nile virus (WNV) is a virus spread by mosquitoes that is found in many countries around the world.

Most cases of WNV are not serious and many people have no symptoms or only mild flu-like symptoms, such as headaches, muscle aches and a high temperature (fever).

Serious problems occur in fewer than 1 in 100 people infected with the virus, but can include infection of the brain (encephalitis), spinal cord, and tissues surrounding the brain and spinal cord (meningitis), which can be fatal.

Signs of a severe infection can include muscle weakness, disorientation, seizures (fits) and loss of consciousness.

You should seek medical advice as soon as possible if you develop symptoms of WNV while you are travelling or after you return home. Make sure you tell the health practitioner where you have been travelling.

Where is WNV found?

Despite its name, WNV is found in many parts of the world, including:

  • Africa
  • west and central Asia
  • The Middle East
  • Europe, particularly southern Europe
  • North, Central and South America
  • The Caribbean
  • Australia

In tropical countries, it's possible to catch WNV all year round. In places with changing summer and winter seasons, such as North America, WNV is usually more common during summer and autumn.

For more information about the area you are visiting, check the Fit for Travel website.

There have been no confirmed cases of WNV originating in the UK, and cases affecting travellers returning to the UK are very rare.

Since 2002, there have only been four cases confirmed in the UK – three in people returning from North America and one in a person returning from the Middle East.

WNV is spread through the bites of infected mosquitoes. Mosquitoes become infected when they feed on infected birds. They can then spread the virus to humans and other animals they bite.

The virus cannot be spread from close person-to-person contact – for example, by kissing someone who is infected.

Diagnosis and treatment

WNV can usually be diagnosed with a blood test. If meningitis is suspected, a sample of cerebrospinal fluid (the fluid surrounding your brain and spinal cord) will be removed during a lumbar puncture and tested.

There is no specific treatment for the infection. If your symptoms are mild, they will usually get better without treatment in a few days and you won't normally experience any long-term side effects.

If your symptoms are more severe, you will need to go to hospital. Treatment may include intravenous fluids (given through a drip in your arm), medication to control seizures, and help with breathing.

Even with treatment, severe WNV can lead to long-term problems such as fatigue (extreme tiredness), muscle weakness and memory problems.

Preventing WNV

As there is no specific treatment or vaccine for WNV, it's best to avoid being bitten by mosquitoes when visiting affected areas. The mosquitoes that carry WNV are most active around dusk and dawn.

You should follow the advice below while you are away:

  • Wear loose-fitting, long-sleeved tops and long trousers that cover up your skin as much as possible.
  • Use an insect repellent on exposed skin, taking care to avoid your eyes. Repellents containing 50% diethyltoluamide (DEET) are thought to be the most effective.
  • Insect-proof screens on windows and doors and mosquito nets impregnated with insecticide over the bed will reduce mosquito bites inside. Air conditioning in the room may also help.
  • Avoid areas where there are likely to be large numbers of mosquitoes, such as near stagnant pools of water.

Read more about preventing insect bites.

West Nile virus develops into a serious condition in less than 1 in 100 people who are infected 

Travel health

Advice for people travelling abroad, including malaria, travel vaccinations, EHIC, travel insurance, DVT and jet lag

Page last reviewed: 19/11/2014

Next review due: 19/11/2016